The present invention relates to improvements in lift truck mounted rotatable clamping apparatus for picking up, transporting and stacking loads, particularly large rolls of paper such as newsprint and kraft paper. More particularly the invention relates to improvements in lift truck clamps capable of performing the three functions of clamping a load, rotating it about an axis longitudinal of the lift truck, and shifting the position of the load generally perpendicular to such axis.
In the past, it has been recognized that it is advantageous for a lift truck-mounted rotatable paper roll clamp to be constructed such that the clamp arms are capable not only of opening and closing (the clamping function) but also of selectively shifting in unison so as to move the load with respect to the lift truck in a direction generally perpendicularly with respect to the axis of rotation of the clamp (the shifting function). The shifting function permits the clamp to be constructed such that the clamp arms are capable of engaging a load, particularly a paper roll, either in a position of equal extension, wherein the forward ends of the clamp arms on either side of the paper roll extend a substantially equal distance forwardly of the lift truck or, alternatively, in a position of unequal extension wherein the forward end of one clamp arm extends a greater distance forwardly of the lift truck than the forward end of the other. The basic desirability of achieving positions of equal and unequal arm extension respectively is that when a paper roll is lying in a horizontal position on the floor or ground, the upper clamp arm must overreach the lower clamp arm in order to grasp the roll to pick it up. Thereafter, if the paper roll is to be stacked vertically by rotating the clamp about its axis of rotation, the overreaching which is characteristic of the position of unequal extension can become an obstacle since both clamp arms should extend the same distance from the truck to place the vertical paper roll in close, compact proximity to other vertical paper rolls. The "unequal extension" position also makes it difficult to remove a vertical paper roll from a compact stack of vertical rolls because of the need to insert the clamp arms between the adjacent rolls. Accordingly, when handling rolls in the vertical position, the position of equal extension of the clamp arms is advantageous.
The above-described shifting function has been provided by certain rotatable clamps in the past, including those shown in Sinclair U.S. Pat. No. 3,896,957, Burton U.S. Pat. No. 3,583,586 and Neale, Sr. U.S. Pat. No. 2,814,396. All of these clamps utilize a pivoted arm construction providing the shifting function and permitting both the unequal extension and equal extension positions. However it should be understood, for purposes of the present invention, that such shifting function and the selective positions of unequal extension and equal extension could also be obtained by structures other than pivoted arm clamps, for example by a sliding arm clamp specially adapted to provide such function.
It should be mentioned that certain types of rotatable sliding arm clamps have been provided in the past, such as that shown in Faust et al U.S. Pat. No. 3,407,951, wherein the position of each clamp arm is controlled by a respective fluid motor independently of the other arm. In some of these previous clamps, the actuation of each arm has been accomplished through a single operator controller interconnected with the two separate fluid motors of the arms through a rotation-responsive valve which determines which fluid motor will be controlled by the single controller, depending upon the rotational position of the clamp. However such clamps cannot perform the above-described shifting function because neither fluid motor is capable of moving the clamp arms in unison, thereby making it impossible to hold the load and shift it in a direction perpendicular to the axis of rotation of the clamp. Since no such shifting of a load during transition between horizontal and vertical load positions can be accomplished with such clamps, equal and unequal arm extension positions cannot be utilized and therefore are not provided.
While the aforementioned pivoted arm rotatable clamps do provide the shifting function for obtaining the alternative positions of unequal extension and equal extension, together with the clamping and rotation functions, they have required special fluid control valve assemblies on the lift truck having three separate operator controllers for the three different functions. However the great majority of existing lift trucks equipped for operating load handling attachments are provided with no more than two separate operator controllers for the load handling attachment. Accordingly the conversion of these existing lift trucks to a rotatable clamp having the above-described shifting function presently involves not only the attachment of the clamp but also the modification of the lift truck's fluid controls, necessitating substantial additional cost for valves, labor to perform the modifications and down time for the lift truck while modifications are being made. Despite the improved operation and productivity obtainable with these clamps having the shifting function, such additional cost, labor and down time can impede their wide-scale adoption by lift truck users.